The invention relates generally to hard disk drives and more precisely to a hard disk drive employing a head suspension assembly with dynamically adjustable head fly height control.
Magnetic hard disk drives include a rotating rigid storage disk and a transducer positioner for positioning a read/write transducer at different radial locations relative to the axis of disk rotation, thereby defining numerous concentric data storage tracks on each recording surface of the disk. The transducer positioner is typically referred to as an actuator. Although numerous actuator structures are known in the art, in-line rotary voice coil actuators are now most frequently employed due to their simplicity, high performance, and mass balance about their axes of rotation, the latter being important for making the actuator less sensitive to perturbations. The in-line rotary voice coil actuator is less susceptible to disturbances external to the disk drive, which can otherwise move the read/write transducer to an unexpected position over the storage disk. A closed-loop servo system within the disk drive is conventionally employed to operate the voice coil actuator and position the read/write transducer with respect to the disk storage surface.
The read/write transducer, which may be of a single or dual element design, is typically mounted on a ceramic slider structure, the slider structure having an air bearing surface for supporting the read/write transducer at a small distance away from the rotating storage disk. Single read/write transducer designs typically require two-wire connections while dual designs having separate reader and writer elements require a pair of two-wire connections.
Sliders are generally mounted on a gimbaled flexure portion. The gimbaled flexure portion is attached to one end of a suspension""s load beam assembly. An opposite end of the suspension""s loadbeam assembly is attached to the in-line rotary voice coil actuator, which provides pivotal motion to the suspension assembly. A spring biases the load beam and the slider with the read/write transducer towards the disk, while the air pressure beneath the slider developed by disk rotation relative to the slider pushes the slider away from the disk. The gimbaled flexure enables the slider to present a xe2x80x9cflyingxe2x80x9d attitude toward the disk surface and follow its topology. An equilibrium distance defines an xe2x80x9cair bearingxe2x80x9d and determines the xe2x80x9cflying heightxe2x80x9d of the read/write transducer. Although the separation between the read/write transducer and disk created by the air bearing reduces read/write transducer efficiency, the avoidance of direct contact of the transducer with the disk vastly improves reliability and extends the useful life of the read/write transducer and disk. The air bearing slider and read/write transducer combination is also known as a read/write head/slider assembly or head.
Currently, nominal flying heights are on the order of 0.5 to 2 microinches. For a given read/write transducer, the magnetic storage density increases as the read/write transducer approaches the storage surface of the disk. Thus, a very low flying height is traded against transducer reliability over a reasonable service life of the disk drive. Increases in data storage densities will require decreases in read/write transducer flying height to near or intermittent contact with a storage surface of the storage disk.
One method of achieving near or intermittent contact recording while minimizing detrimental effects, such as reduced head life, is illustrated in xe2x80x9cAn Active Slider For Practical Contact Recordingxe2x80x9d,IEEE Transactions On Magnetics, Vol. 26, No. 5, September 1990. The active slider design includes active material inserted into a channel that runs across the full width of the slider at its top rear. Two deep slots formed on the rear of the active slider body define a rear central bending portion, which bending portion is mechanically and electrically isolated from the outer air bearing rails of the slider. When a voltage is applied to the central active material, the material expands in the direction of the electric field. The rear central bending portion of the slider, which is positioned under the active material, constrains this expansion and, as a result a bending moment develops which causes the rear central bending portion of the slider to bend and move downward, toward the rotating storage disk. As a result, a read/write transducer mounted on the rear central bending portion of the active slider is moved to a near or contact relationship with the rotating storage disk.
One problem with the above described active slider for practical contact recording is that the slider body must be modified to include the channel that runs across the full width of the slider at its top rear. Further, the slider body must be modified to include the two deep slots to form the central bending portion. Forming the channel and the two deep slots is undesirable because of the additional wafer process steps introduced to the already time intensive slider wafer fabrication process.
Additionally, the disk drive industry has been progressively decreasing both the size and mass of slider structures to reduce the moving mass of the actuator assembly and to permit near or intermittent contact operation of the read/write transducer with the disk surface. The former gives rise to improved seek performance and the latter gives rise to improved transducer efficiency and higher areal density, but at a cost of reduced transducer reliability. Slider body miniaturization further precludes the use of the above described active slider because the slider body is no longer large enough to accommodate the channel and deep slots required by the active slider. Typically, minimization in slider body size (and therefore mass) is characterized with reference to a so-called standard 100% slider (xe2x80x9cminisliderxe2x80x9d). The terms 70%, 50%, and 30% slider (xe2x80x9cmicrosliderxe2x80x9d, xe2x80x9cnanosliderxe2x80x9d and xe2x80x9cpicosliderxe2x80x9d, respectively) refer to more recent low mass sliders that have linear dimensions that are scaled by the applicable percentage relative to the linear dimensions of a standard minislider. Sliders smaller than the 30% picoslider, such as a 20% xe2x80x9cfemtosliderxe2x80x9d, are presently being considered and are in early development by head vendors.
Another problem that arises as a result of decreases in slider body sizes is that smaller sliders generally require gimbaled flexure portions that have consistent gram loads and intrinsic stiffness. Variations in the gimbaled flexure portion intrinsic stiffness cause sliders (and consequently the read/write transducers) to fly at different heights. Because the efficiency of the magnetic recording process changes significantly with the fly height, variations in fly height result in corresponding variations in recording storage densities. Because it is practically impossible to know the flying height variation of any given slider with any given read/write transducer, multi platter disk drives typically record data at less than optimal storage densities to allow for the variations in flying heights of the sliders incorporated therein. This lowers the overall storage capacity of the multi-platter disk drive.
Thus, a hitherto unsolved need has remained for an apparatus that compensates for variations in the mechanical properties of gimbaled flexures that influence slider fly height.
An objective of the present invention is to provide a suspension assembly having a gimbaled flexure portion for supporting a head adjacent to a rotating storage disk, where the flexure portion""s pitch and/or roll are dynamically adjustable for controlling the flying height of the head. When the head is not reading data from or writing data to the disk, the flying height of the head is adjusted to be relatively high with respect to the rotating storage disk for minimizing head/disk contact to reduce the wear on both the head and the disk. When the head is used to read data from or write data to the disk, the head is adjusted to have a relatively low flying height with respect to the disk, allowing an increase in the storage density of the storage disk.
Another objective of the present invention is to provide a suspension assembly having an adjustable flexure portion pitch angle to compensate for variations in intrinsic stiffness between suspension assemblies which are then incorporated into multi-platter disk drives.
An embodiment of the present invention comprises a suspension assembly for supporting a head adjacent to a rotating storage disk. The suspension assembly comprises a generally elongated loadbeam with a first end and a second end. A baseplate is defined at the first end of the loadbeam and a gimbaled flexure portion is attached to the second end of the loadbeam. The baseplate includes a central bore for attaching the first end of the loadbeam to a head arm of a rotary actuator assembly. The gimbaled flexure portion includes a pair of upwardly curved flexure legs extending from a flexure tongue. The free end of each flexure leg is attached to the loadbeam.
The top surface of the flexure tongue contacts a load dimple formed on the bottom surface of the loadbeam for enabling the tongue to pivot about the load dimple. The head is attached to the bottom surface of the tongue, where pivotal motion of the tongue is transposed to the head for adjusting the pitch of the head with respect to the rotating storage disk.
A pair of thermal-expansion strips is coupled to the gimbaled flexure portion. In attaching each of the thermal-expansion strips to the flexure portion, a first end of each strip and a second end of each strip is securely attached to the flexure portion, leaving the body of the strip unconnected and free. Each thermal-expansion strip is coupled to a separate power source via a power conductor defined along the elongated loadbeam. During use, the power sources provide electrical current to the thermal-expansion strips, causing the strips to elongate. This elongation of the thermal-expansion strips is transposed to the gimbaled flexure portion, bending the flexure portion, with attached head, down. Thus, the pitch angle of the head is adjusted so that a read/write transducer incorporated at the trailing edge of the head is minutely moved downward and toward the rotating storage disk. As a result, the flying height of the read/write transducer, which is incorporated within the head, is reduced with respect to the rotating storage disk.